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Selecting Binoculars for Birding Part 01


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Author Topic: Selecting Binoculars for Birding Part 01  (Read 1296 times)
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« on: January 17, 2010, 03:44:16 am »

Most birders have one pair of binoculars that must serve under a wide range of viewing conditions. Some birders prefer having a larger pair that gathers the maximum amount of light for owling and other low-light situations, and a lighter weight pair for more typical daytime conditions. But most birders take the same pair along no matter what they’re viewing, and so it’s important to select binoculars with all your viewing needs in mind.

How far can you see through binoculars?

If you’re viewing the night sky with binoculars, you’ll be able to see more stars with binoculars than without. And with binoculars you’ll be able to resolve individual birds in a flock to count them at distances from which you simply couldn’t resolve the individual birds with your eyes. But overall, you’re not going to see farther with binoculars than you can with your own eyes. What you will be able to do is bring birds closer, so you’ll be able to resolve many details you couldn’t see with your naked eye. Binoculars also do something else—they narrow your field of view to help you focus all your attention on one thing at a time. When I’ve been at evening slide programs with other birders who came in after a day of birding, I’ve always been surprised at how many of us automatically pull up our binoculars to better view the details of birds on the screen, even though they’re already huge. This is reflexive—after a while birders simply do this whenever we see a bird without even thinking about it. Why use binoculars when we can see it just fine through our eyes? When we look at anything through binoculars, we don’t see anything outside of the binoculars’ field of view to distract us. This focusing of our attention as well as our eyes becomes second nature.

Every pair of binoculars is described by two numbers, such as 8x42 or 10x50. The first number refers to the magnification. The second number is the diameter (in millimeters) of the objective lens (the larger, front lens).

Virtually all birding binoculars are 7x, 8x, or 10x, though a few birders use binoculars up to 15x. There are advantages and disadvantages to each. The higher the magnification, the more detail you see and the bigger the image you’re looking at. Even though the differences are technically significant, in 90 percent of your viewing situations, the power of binoculars won’t make a difference in your ability to find and identify birds.
The smaller your magnification, the more of the scene you will see and, for the same size glasses, the brighter your image. When weders -counting, 7x binoculars can show a few more Weders in the sky at a given moment than 10x do. Also, when a bird is moving quickly, you have a better chance of actually finding it in the field of view using lower-power glasses. And lower-power binoculars can focus closer than comparable higher-power models.

The higher the magnification, the worse the effects of heat shimmer and any hand shaking. Also, for otherwise comparable binoculars, the higher the magnification, the heavier the binoculars, the harder to focus on close objects, and the more rotations of the focus wheel to go from near to far. Very few advanced birders use 12x or higher because of the small field of view, the difficulty in holding them steady, their low light, and their heavy weight. And very few advanced birders even consider zoom binoculars because the zoom mechanism compromises optical clarity (though not nearly as much as in the past when manufacturers used less advanced coatings). Zoom binoculars are also heavier than comparable standard binoculars. Image stabilized binoculars make up for the shaking and distortion, but are bulkier and weigh more than comparable non-stabilized models.
Birders who also enjoy dragonflies and butterflies often select 7x binoculars for their closer-focusing capabilities. Birders who watch owls or other birds most often seen in low-light or night conditions also prefer 7x or 8x. 
Birders who watch Eagles have to balance the extra detail they get from 10x with the larger field of view (which can include more Eagles in a single image) seen through 7x.

One other consideration about magnification is that any flaws in the design or optics of a line of binoculars will be increased at higher magnifications. If a focus wheel needs a lot of adjustments on a 7x pair, it will need even more adjustments on a 10x pair. If low power binoculars are not particularly bright, higher power binoculars in that line will be dimmer. I’d never consider 10x binoculars in inexpensive lines—to get the best quality for the money, lower power would definitely be wiser. Of course, to get the most value in any line of binoculars, lower power glasses are virtually always significantly less expensive than higher power glasses of comparable quality.
Because of the tradeoffs, the majority of birders who have just one pair of binoculars prefer 8x binoculars, but there are excellent, advanced birders using each power, even 15x. If you aren’t sure which you prefer, try to compare them in the field. You can try out other people’s binoculars when you go on field trips, or test various models at vendor displays at birding festivals.

Diameter of Objective Lens
The second number describing binoculars refers to the diameter of the objective lens, measured in millimeters. Pocket or compact binoculars usually have smaller than a 32 mm lens and some are as small as 18 mm. This makes them wonderfully easy to carry around in a purse or pocket. To offset this advantage, they’re uncomfortably small for many hands and don’t work well under low light conditions.
You really do need something bigger to see owls, or other birds under the lowlight conditions they’re usually seen in.
Binoculars with an objective lens over 50 mm let in enormous quantities of light, an advantage offset by their extra weight. Many birders now use a binocular harness rather than a neck strap, and this is especially helpful with large binoculars.

Most standard binoculars have an objective lens between 35 and 50 mm. Since magnification power also affects how bright your image is, a single line of binoculars tends to have larger objective lenses as the magnification power goes up. The general rule when I started birding that to get decent light-gathering you needed binoculars with a second number at least five times the first number (i.e. 7x35, 8x40, 10x50). But as the quality of lenses and coatings has improved, that rule no longer holds true, especially for high-end and even many mid-price binoculars. But a great many birders believe that the ideal binoculars are 8x40 or 8x42 because of their relative light weight for optimal light gathering capabilities.

 Exit Pupil and Optical Quality
The Exit Pupil is a number describing the magnified image in the eyepiece as it leaves the binocular to enter your eye. You can figure out what it is by dividing the size of the objective lens by the magnification power. That is, 10x50 binoculars would have an exit pupil of 5mm, and 7x42 binoculars would have an exit pupil of 6mm. You can judge both the size of the exit pupil and the quality of binocular optics by holding the binoculars at arm’s length and looking at the spot of light in the eyepiece. The larger it is, the larger the exit pupil. Exit pupil is one indication of how well you can see at twilight or at night. Brightness of the image is also greatly affected by the quality of the glass and the coatings, but an exit pupil of at least 4mm is important if you ever bird in twilight or shadowy conditions. This is why pocket binoculars aren’t the best choice for low-light birding. 8x40 binoculars have an exit pupil of 5, and 8x42 are even better for superior light gathering.

While looking at the light spot to judge the size of the exit pupil, pay close attention to how crisp it is. The sharper the edges, and the more perfect a circle, the higher quality the optics. To test whether the binoculars are properly aligned, hold them out or, better, set them on something level, pointed at a straight horizontal line such as a shelf, the line between a wall and ceiling, or a distant building. If the binoculars are truly aligned, the line should be at precisely the same level in each of the eyepieces.

Eye Relief
One number that usually isn’t featured conspicuously on binocular specifications but can be very important if you wear eyeglasses is Eye Relief. This is the measurement, in millimeters, of the optimal distance between your eyeball and the ocular lens of the binoculars. Binoculars virtually never have the eye relief written on them, but you can make a rough estimate by simply looking at the eye cups. Manufacturers design their eye cups to hold the binoculars at the right distance from the naked eye. No matter what the eye relief is, if you don’t wear eyeglasses you can extend the eye cups and they’ll be set at the proper distance for you. If you and everyone else who uses your binoculars don’t wear eyeglasses, eye relief won’t matter at all.
But if you do wear eyeglasses, you want to make sure that the eye relief is about the distance from your eye to the outer surface of your eyeglass lenses. Glasses with thick lenses or frames that hold them well out from your eyes require binoculars with longer eye relief than glasses with thin lenses in frames that are close to your eyes.
How do you figure out what the best eye relief for you is? If you have an opportunity to test out several different binoculars with different eye relief, you can see what the specs are on the binoculars that work best for you. Otherwise, you may simply have to make an educated guess. If you wear small, close-fitting glasses, an eye relief of 14 or 15 should be right. If your glasses are thicker and/or farther fitting, try 16-18.
Even if the eye relief doesn’t properly match your glasses, you’ll still be able to see through binoculars. But when the eye relief is shorter than it should be, your field of view will be narrower and the image will not be as large as it would be with proper eye relief–this is often called “tunneling” or “tunnel vision.” If the eye relief is longer than it should be, you may find yourself holding the binoculars slightly out from your glasses, making them harder to hold steady. Fortunately, more and more binoculars are coming with adjustable eyecups, allowing you to extend them slightly if necessary to hold them at the perfect distance from your eyes.

Binocular design
At the same price point, the optics in porro prism binoculars are simpler and so usually higher quality than roof prism binoculars, so in lower price lines, porroprisms are sometimes the wiser choice. They tend to have good light gathering and depth of field, though they’re heavier, bulkier, and have an external focus, making them more vulnerable to water and dirt damage.
Remember that the more you spend on binoculars relative to what you can comfortably afford, the more protective of them you’ll be and the more reluctant to bring them canoeing or biking. You’d see way more birds through more affordable binoculars you’re comfortable bringing everywhere than you’ll see through the finest quality optics that you leave at home. But also remember that inexpensive binoculars may not be as durable. When binoculars are knocked out of alignment, they can cause eye fatigue and headaches, especially if you use them for long periods.

Depth of Field
Binoculars that are “auto-focusing” maximize the depth of field, meaning you are constantly focused on both near and far. The trade-off is that visual acuity at every distance is sacrificed. A precise focus adjustment is far better for getting the level of clarity that birders need. But for birding, you also want to be able to switch almost instantly from a nearby sunbird to distant Eagles. The more turns on a focusing knob you must make to switch from near to far (or vice versa), the more birds you’ll miss. And the more focusing adjustments you need to make to keep a single warbler in view as it flits from branch to branch, the more frustrated you’ll get. When comparing binoculars, see how many pushes you need to give the focusing knob to go from near to far with each model, and see how easy it is to stay focused on a moving bird.

Field of View

Field of view is given either as the width of your view at 1000 feet, or as a number of degrees. Wide angle binoculars give you a wider field of view, making it easier to locate birds when you’re inexperienced at using binoculars, but unless the binoculars are expensive, the added field of view is often blurry. Wide angle binoculars are heavier than comparable standard ones, and sometimes not quite as crisp. Most birders prefer standard binoculars unless they do a lot of work counting birds in the sky. Even when I was counting flocks of migrant bird.

Close Focus
Many birders are now also looking at butterflies and dragonflies, which are often only a few feet away, and so “close focusing” binoculars have become very popular. But close-focusing within a few feet comes at the cost of some optical clarity and having to make more corrections with the focus knob to keep things in focus. If you want this feature, make sure to test how easily you can switch from looking at something close to something far.
« Last Edit: January 19, 2010, 04:48:11 am by indunil » Report Spam   Logged

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